Results of this study will provide sufficient information to determine the fractional contribution of gastrointestinal and hepatic biotransformation to the overall presystemic elimination or morphine which will improve our understanting of the in vivo diodisposition of morphine. A comprehensive pharmacokinetic-pharmacodynamic model for morphine and the metabolites, M3G and M6G, will be developed. This model will be sued to determine equi-analgesic doses of morphine adfministred by various routes.